Primary keys and foreign keys in Supabase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a primary key in a database?

A primary key is a unique identifier for each record in a table. It ensures that no two rows have the same value in this column, helping to find data quickly and avoid duplicates.

beginner

What is a foreign key in a database?

A foreign key is a column in one table that links to the primary key in another table. It helps connect related data across tables, like linking a customer to their orders.

intermediate

Why are primary keys important in Supabase tables?

Primary keys in Supabase ensure each row is unique and can be referenced by other tables. This helps keep data organized and supports relationships between tables.

intermediate

How does a foreign key enforce data integrity?

A foreign key makes sure that the value in one table matches a valid primary key in another table. This prevents invalid or orphaned data, keeping the database consistent.

intermediate

Can a table have more than one foreign key? Explain.

Yes, a table can have multiple foreign keys. Each foreign key links to a different table, allowing complex relationships like an order linked to both a customer and a product.

What does a primary key guarantee in a table?

A Each row is unique

B All columns are unique

C Data is encrypted

D Table has no rows

A primary key guarantees that each row in the table has a unique value in that column.

What is the role of a foreign key?

A To uniquely identify rows

B To speed up queries

C To store large files

D To link tables together

A foreign key links one table to another by referencing the primary key.

In Supabase, what happens if you try to insert a foreign key value that does not exist in the referenced table?

A The insert succeeds

B The foreign key is ignored

C The insert fails with an error

D The referenced table is updated

Foreign key constraints prevent inserting invalid references, so the insert fails.

Can a primary key column contain NULL values?

A No, primary keys must be NOT NULL

B Only if the table is empty

C Yes, always

D Only in foreign key columns

Primary keys must have a value for every row; NULL is not allowed.

Which of these best describes a composite primary key?

A A foreign key referencing multiple tables

B A primary key made of multiple columns

C A key that encrypts data

D A key that allows duplicates

A composite primary key uses more than one column to uniquely identify a row.

Explain in your own words what primary keys and foreign keys are and why they matter in a database.

Think about how you would organize a contact list and link it to messages.

Describe how foreign keys help keep data consistent when you have multiple tables in Supabase.

Imagine you have orders and customers in separate tables.